


Forbidden Rendezvous

by Dark_Crystal_Demon



Series: Forbidden [2]
Category: Undertale (Video Game)
Genre: BDSM, Bondage and Discipline, Complicated Relationships, Consensual Kink, Consensual Non-Consent, Consensual Sex, Daddy Kink, Dom Muffet, Dom Sans, Dom W. D. Gaster, Dom/sub, Ecto-Penis (Undertale), Ecto-Tentacles (Undertale), Emotional Manipulation, Master/Pet, Multi, Polyamory, Sub Papyrus, Sub Sans, Switch Sans, Though Some is Ignorant Consent, sub Reader
Language: English
Status: In-Progress
Published: 2017-03-17
Updated: 2017-03-17
Packaged: 2018-10-06 13:36:05
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,530
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10335797
Author URL: https://archiveofourown.org/users/Dark_Crystal_Demon/pseuds/Dark_Crystal_Demon
Summary: It's time for you to learn the rules of being a pet to our favorite skeletons.Unfortunately, you've never been good at following rules. And Sans... well, he's a bad influence.But did Gaster really bring you into the family just for companionship?Science, sex, complicated relationships, manipulations, puzzles, and a look into the void.Welcome to Part 2 of the Forbidden Series!





	

**Author's Note:**

> This chapter starts right after the ending of [part one](http://archiveofourown.org/works/8920258/chapters/20432434). I recommend reading that first.

When you get out of the limo, you wonder how deep you are underground. The walls of the private parking garage are jagged rock with a blue glow from fungi and flowers you've never seen before. In the distance, you can hear a subterranean river rippling somewhere in the dark passages that lead to... where?

Has this really existed underneath the lab the whole time you've been working in here?

Sans clears his throat; or, rather, makes a noise deep in his skull to get your attention. He's a skeleton. He doesn't have a throat. But you're realizing how clever skeleton monsters are at picking up on human actions and emulating them for your benefit. _Could that be regarded as manipulative or considerate?..._ you shake your head and push the thought of the former to the back of your mind. 

"The, uh, Doctor never got used to being above ground," Sans explains, watching your wondering eyes. He takes your hand in his. He's shaking. From excitement or fear? Little puffs of cold air appearing by his teeth. How? Why pretend to breathe when you don't have lungs? 

The smell of Gaster's cigarette smoke clings to both of you. 

There's still so much you don't know about skeletons. 

You look around the unfamiliar lot. There's still so much you don't know in general. And there is only one way to fix that. You nod towards the support columns that are carved with intricate designs and strange block lettering. "What do the runes mean?"

"It's the history of the war between monsters and humans," Sans answers solemnly. 

"Why would he-?" _want to read that right as he exits the lab?_ The words catch in your throat from the implication, but Sans understands.

"Because Gaster never forgets," Sans squeezes your hand, a blue glow flashing for a moment in his left eye socket. "You still have time to run. I can't guarantee your safety, kid."

"We've already had this conversation," you shake your head, knowing the decision is foolish but unable to turn away. You don't know much about Dr. W. D. Gaster. This is a chance to see into the world of a genius scientist. Sure, it'll be as a pet. But, if you were honest with yourself, "pet" is exactly how you feel next to the man who literally wrote your textbooks and completely changed the scientific world's perception on dark energy and matter theory.

Handling Gaster's rough kink would be a small price to pay for access to that kind of knowledge. 

Sans lets out a small sigh and mutters something about determination. You walk up to the entrance of your new home. But the set of double lab doors don't open. 

"You'll need to wear this to get in and out of the lab," Sans pulls out a black leather collar from his jacket. It has a tiny red bell and metal loops along the strap. You wonder how he kept that in his jacket without the bell jingling. But before you can ask, he points to the camera above the door and continues his explanation, "Entrance is only allowed for family members. This collar has a chip that recognizes you as our pet. You can only leave with this and one of us at your side."

"Not alone?"

"Pets aren't allowed to leave the house alone."

You stare at the collar and think about the restrictions of your new role. Pet. "Bunny." They really took this role play seriously. You wonder if Laeloni has similar rules with her pets, and then feel guilty for thinking of your girlfriend...  _Former_ girlfriend. 

Would she understand why you aren't coming home? Would she hate you for wanting this life, but not with her as your master? You wouldn't blame her for hating you. Ambition has always been your weakness and now... you've found another.

You lift your hair and bare your neck, still bruised from the Gaster's tentacles. Sans kisses along the bruises before he places the leather around it. You blush under his gentle touch. You didn't deserve it after what you've done. But the warm buzz of his magic erases your guilt as it filters into your body and rushes through your nervous system. Your lips part with the sensation. His face is so close to yours. The tips of his phalanges caress the nape of your neck while they fasten your collar.

When he finishes, he runs his hands up your neck, to the base of your jawline. His magic floods into you, leaving you light-headed. His voice catches in a chuckle as his mouth inches closer to yours. "Pet, I think... you might be a magic addict."

You stick out your tongue, licking his mandible. It sends an electric shock through your body, and you hum with it. "I think you're right, master _._ " You wrap your arms over his shoulder bones and his hands instinctively wrap around your waist, pulling your hips against his. "Though," you grind against him, feeling him hard beneath the fabric of his pants. "I can think of a few other things I'm addicted to."

He kisses you more passionately that he did before in the limo. You feel his magic surround you as the kiss continues. It leaves you breathless.

"You are my addiction," Sans whispers against your mouth. His sincerity wakes you up from the magical buzz in your head. Your eyes look into the lights within his. There's so many emotions trapped within his expression. Need. Guilt. Sadness. And... something neither of you have said. Forbidden like the kisses you couldn't indulge in until now. "My bunny, I never wanted to share you."

The lab doors slide open suddenly and surprise you both. You jump out of Sans' arms in fear of Gaster's disapproval, but Gaster isn't on the other side of the door. Instead there is a... butler. Black suit, white gloves, in one hand he is holding a silver plate with a domed metallic cover. The other hand glides over his thin, gray, dead looking skin that covers his head. It's like he is trying to push back hair that doesn't exist. You wonder if he used to have hair, and if it disappeared with the rest of his face. No nose, no eyes, no ears. Only a wide mouth that stretched further than it should across his barren face. 

He walks out of the building with a eerie grace for someone without eyes. He even faces you, and welcomes you with a sweeping bow. The dish in his hand stays perfectly balanced, still and unmoving, like a fixed spot in space. It's an admirable skill and you wonder what's under the dome. Snacks? Drinks? But he doesn't offer you anything.

"Oh, I am sorry. I did not mean to interrupt," he smiles, revealing a set of horrifyingly sharp teeth. You shiver at the display, and he smiles wider in response. "The Doctor asked me to show our new _bunny_ to her room."

When he says your name, the full extent of his teeth are revealed in a demonic smile. You know monsters come in all shapes and sizes. Some look more dangerous than they are. But you don't want to be left alone with this one quite yet.

Sans puts an arm around your waist and leads you forward passed the butler. "No need, Duo. Her room is right next to mine. I can take her. Besides, dad wants me to clean her up."

"As you wish, Master Sans. His will be done."

"Yeah, his will," Sans shrugs, winking at you as you both cross the threshold. Your collar bell jingles. You stop mid-step in awe at the full view of the foyer inside. It's vibrant, rich color fills your vision. Sans whispers in your ear, "The king wanted everyone to remember that the Doctor is a _royal_ scientist."  

"Oh wow, is that-?"

"A grand staircase spiraling around an incandescent tube full of multi-colored light? Yes."

"What is it?"

"The barrier. Well, what's left of it. The spell had blocked the entrance of the cavern for so long that part of the magic had fused with the rock. Doc removed all the rocks he could find and then, with a little energy push, he brought it back to life."

"As a decoration?"

"As a reminder," Sans' eyes narrow, but then he flashes his casual grin. "It's a pet project he studies every now and then when he gets bored. He's still not convinced the barrier couldn't have been broken some other way. Now," he sweeps your legs out from under you and catches you in his arms. Your bell jingles again. "Let's show our new pet to her room."

You giggle and kiss Sans' cheek as he carries you up the stairs. Movement catches your eye behind Sans. Duo is walking back into the building... but he's doing it backwards. As you move up the stairs, he raises his tray higher, but he doesn't turn around. As you reach the second floor and walk across the balcony to the bedrooms, he turns his tray, as if he was turning his head. You breathe a sigh of relief when he's no longer in view. "That guy is kind of creepy."

"Duo?" Sans laughs as he opens one of the many doors in the hallway and takes you inside. "You just fucked a monster that secretes the essence of the Void itself, but you're worried about Duo?"

There is a bite to his comment, a tension in his bones, as he talks about Gaster. You kiss his cheekbone. "Is Gaster really your dad?"

"It's more complicated than that." Of course it is. He sets you down on the plush, purple carpet of the aptly named "purple room" that was now your own. You'd look around, but at this moment, it feels more important to keep your eyes on Sans. He'd watched Gaster take you... body and soul. You both were going to have to talk about it. But this whole night feels like a dream that your consciousness is only slowly beginning to wake from. The void Gaster took you to still lingers at the edges of your vision.

You take off your red dress, collar bell jingling, and stand naked before your lover. "Let's wash every inch of him off me."

A small smirk appears on his face. "He won't like hearing things like that."

"Is he listening right now?"

"No, though he would have you believe that he's always listening."

"And if he was listening," you walk up to Sans, slipping your hands underneath his shirt. He gasps in response as your fingers explore the thick bones of his spine and rib cage. The magic of his body calls to you. "What would you want him to hear?"

You wrap your hand around his xiphoid, but he winces in pain. "Sans?"

"It's nothing."

You lift his shirt and gasp. Sans sighs, and reluctantly pulls off his shirt and jacket to reveal his naked bones above his waistband. His bones are covered with tiny, shallow cuts. Most of them are nearly imperceptible, thin, like they were done by a scalpel. But there are so many of them... "He wanted to make sure we both had a reminder of what happens when you don't answer his texts."

"Oh Sans, I'm so sorry," tears well in your eyes. This is what happened to him these last few days? This is why he's been missing...

Sans encircles you in his arms, the cuts in his bones pressing against your skin. "Shhh," he whispers in your ear. "What if I..." he hesitates and then pushes forward, revealing a secret he's never told you. "What if I told you that I enjoyed it?"

There is a long beat of silence. The tension in Sans' bones is at its apex. You can feel him tremble, waiting for your response.

And what will be your response? His unspoken question lies heavy between you: Will you still find him attractive? A master who switches when he's with another?

You'd thought his tense demeanor had been only about finding you with Gaster. Now you understand that he had been dreading _this_ moment. The moment Gaster set up for you. The moment you realize... _you're not the only one who likes to be punished._

You close your eyes and let your hands move on their own. You delicately trace the thin grooves left by Gaster's scalpel. Sans' breath shakes against your skin. You press harder, and his breath catches. The magic trying to repair his bones latches to your fingers, stinging them in defense with a brilliant shock that leaves your skin tingling in delight. His body has become even more invigorating than before. The way he clutches at your skin...

"Master," your words relax the rest of his body as you continue to address him as your dominant. _Did you really think I wouldn't want you after I had had him?_ you think, but instead you turn the script back to him, giving him the power while you continue to explore the new weaknesses carved into his body. "Do I... still please you?"

Like the jingle of your bell through the air, his smile rings into your heart. 

 _Yes, Bunny._ He kisses you, like he's trying to send you the answer through pure will alone. His body presses harder against yours. The cuts in his bones making them sharp. It feels like his body is biting into yours, hungry nips along your breasts, against your stomach. It feels good. It feels like the first time all over again. Your bodies exploring each other. You moan his name, and he moans yours as your fingers learn new tricks.

Your skin reddens as you continue to grind against each other. What would Gaster say when he saw all these tiny scrapes along your body?

Your body marked by Sans' punishment. Would he be jealous that he wasn't here to watch? Or would he smile knowing that you were thinking about him right now.

His presence is etched between you like the smoke that still hangs in the air and enters your lungs.

You pull Sans harder against you, trying to wipe Gaster's smile from your mind as Sans' magic tingles your skin. His moans caress your ear as he bites down on your sensitive skin.

"You feel so good, Bunny. I've missed you," he pulls one of your legs up to his waist. You wrap the rest of your body around him, letting him carry you. With his hands firmly clutching your ass, you feel the tip of his penis poking through the top of his low waistline. Its smooth, wet tip caresses the inside of your legs. You arch your back, rubbing it against your wet entrance. He growls and claims your mouth, biting down hard on your lower lip, almost drawing blood. 

You continue your grind, gripping the back of his thick spinal cord as his fingers tighten around your body. He gasps when you thrust harder against him. It makes you feel playful. "Am I hurting you, Master?"

"Yes, don't stop." Your legs are getting covered in his precum. You try to push down his pants, but they're stubborn and teasing you. You want him inside you. Now.

"Master, you're supposed to be getting me clean. I'm going to tell the Doctor you didn't follow his orders."

He smiles against your mouth. "Are you threatening me with a good time?" He starts to walk you both to the bathroom. Like the rest of the house, it's absurdly large and elegant with both a walk-in shower and a large Jacuzzi tub inside it. He chuckles, "Maybe I should tell Doc that you didn't need a shower. You were wet enough without it."

"I need a thorough scrubbing. I've been very dirty."

"Indeed," Sans' voice growls, as he slams you into the tile of the shower wall and turns on the hot water. You yell out as it scolds you, but then his bones block the direct blast. Streams of hot water drip over your skin through his rib cage. You bite your lip in anticipation as his pants begin to sag from the weight of the water. Soon it frees him entirely, his pants pooling around his ankle bones. His tip teases your entrance. You try to push him inside, but Sans is stronger.

His earlier uncertainty has been replaced with the intoxicating confidence. "Why should I fuck my father's sloppy seconds?"

"You'll never be second." The truth of your words makes his eyes lock onto yours. You unbuckle the collar around your neck and toss it to the ground outside the shower. "You'll always be my first, Master."

"You're going to get me into a lot of trouble."

"Mmm, I bet you'll like that, Master." You grab hold of his ribs roughly. He arches his back reveling in the pain. His tip pushes just inside your lips as he does. You bring your mouth to his clavicle and lick a particularly thick cut, almost slicing open your tongue against his rigid groove. His moans echo against the walls of the shower. You take advantage of his distraction and slide the rest of your body down his thick shaft. "Ah! Mmm. Oh, Master.... Opps, did we just break a rule?"

"Ah! You, naughty bunny," Sans staggers as your mouth continues to suck and lick on his bones. You circle your hips, pushing him deeper inside you. He stops your movement with a forceful push against the tile. You yell out as he grows inside you. His girth doubling, nearly splitting you in two. Your body stretches around him, trying to accommodate his new size. You bang your head back against the tile, almost knocking yourself out in your excitement. Tears well in your eyes, but the only thing your mind can focus on is him, massive and pressing you to your limits. His deep voice filling your mind, "Is this what you wanted pet? You're so tight. Mmmm. So obedient, taking me all inside you. But I think you can handle more."

"No-AH!" He stretches you further, pushing deeper.

"No? Don't you want your other master to know I was here? I'll stretch you out so that the next time he's here he'll know," He thrusts deeper and you cry out again in a mixture of pleasure and pain. Sans voice growls in his possessiveness. "He'll know you run to me."

You can't answer. Your breathing is ragged as every part of you screams in disbelief of how much of him is inside you. He's never pushed it this far. He begins to pull out. You whimper.

"I'm sorry, pet. I didn't hear you."

"Please." You feel hollow as all but his tip leaves your body.

"Please what?" He circles his hips, imitating your earlier tease.

"Please don't stop, Master."

"Haven't you had enough?"

"No."

"He wasn't enough for you?"

"No. Only you're enough for me."

He rewards your words with a thrust that nearly breaks the tile behind you. You yell out his name in thank you.

"Louder," He bites your neck where the collar was. You feel him break the skin. He picks up his rhythm as your moans echo against the shower tile. "Louder."

"AH! AH! SANS! YES!"

"Louder, pet. Let him know how deep I'm cleaning you."

You obey, yelling his name louder as every thrust fills you. The warm water of the shower caresses your body through his rough, thick, bones.

You lose track of time as he carves himself into you like the cuts along his bones. 

You scream in joy until your voice leaves you as you cum. Your silent, shaking body, only drives him into a primal pounding, elongating your orgasm as you ride along his passionate thrusts. 

He cums with a roar, filling you with his magic. You imagine it traveling across your entire body, covering your soul with his cum, cleansing it of the darkness Gaster left there.

You pant, leaning against each other as the water continues to rain down over your bodies. 

"Bunny, I-"

"Ahem!" Your body stiffens at the new voice inside the room. Sans doesn't turn around. He keeps you encircled in his arms. His cock still inside you. 

"What do you want Duo?" Sans growls. You can't see the butler from the alcove wall of the walk in shower. You're grateful for the wall. You didn't need to see that smile while you were so vulnerably naked.

"The Doctor sent me to tell you it is ten... now eight minutes until dinner, Master Sans."

"Tell Gaster we'll be a bit late. The bunny was dirtier than expected. She needed a lot of cleaning." He kisses you.

"The Doctor will not like that response." Was that a tinge of fear in Duo's voice?

"He can punish me for it later," Sans grins. You hear Duo take his leave with a huff. 

You knock your forehead against his as he continues to hold you in his arms. "I'll lick your wounds when he's done."

"I wasn't going to give you the choice not to."

**Notes for the Chapter:**

> Thank you for your patience! I know this is a very late edition to the Valentine's Challenge, but it seemed only fitting to keep with the challenge themes since part 1 was a winter holiday one. 
> 
> So... what did you think? 
> 
> "Duo" is a non-cleverly named version of Gaster Follower Number 2... well, almost clever when you think about what's in that domes platter he carries around...
> 
> No Gaster or Laeloni in this chapter, but you'll see them prominently in Chapter 2. I wanted Chapter 1 to bring us back to the two who started this whole affair... ^_^ 
> 
> Really those two just can't stay out of trouble...What do you think their punishment is going to be?
> 
> Speaking of delicious punishments, check out my Tumblr for more wonderful NSFW moments and Undertail recommendations: [Dark_Crystal_Demon](https://www.tumblr.com/blog/darkcrystaldemon)


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